This project intends to describe the pharmacokinetics of aminoglycoside antibiotics in infants and children with different routes of administration. Children with cystic firosis are particularly targeted for study. Antibiotic dosage regimens will be tailored, using the pharmacokinetic parameters as guidelines. Efficacy of the drug will be assessed in terms of bacterial density at the foucus of infection, magnitude of the local inflammatory response, the function of the organ system involved and clinical indices. Toxicity will be monitored by serial testing of target-organ function. Novel means of identifying and reversing toxicity will be examined.